[RPD-314] Remove non-modular Terraform files

[Christopher-Norman]

This PR removes:

• infrastructure/llm directory
• infrastructure/default directory
• LLM_STACK and DEFAULT_STACK lists from azure_runner.py

as they are no longer required. In this PR we also update the AzureRunner __init__ function to take no parameters as the existing parameter is no longer required.

Checklist

Please ensure you have done the following:

• I have read the CONTRIBUTING guide.
• I have updated the documentation if required.
• I have added tests which cover my changes.

Type of change

Tick all those that apply:

• Bug Fix (non-breaking change, fixing an issue)
• New feature (non-breaking change to add functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Other (add details above)